Employee Rights

Employees have the legal right to refuse to be tested (or to enter
rehabilitation), but this will usually result in their termination.
Legal consequences rarely stem from a positive drug test, as a drug
test does not itself meet the legal standards for evidence in a
prosecution. In addition, most employers will prefer to keep the
matter quiet, as businesses are occasionally sued by disgruntled
employees who consider their privacy to have been violated by random
testing.
http://www.getgift.com.cn/Drug-Testi...-Workplace.htm